Narrow (wideband) impulses for use as a driving signal(s) for various applications is generally know per se. Typical examples are, for instance, UWB communication, radar such as through the wall imaging, Comb generator, frequency multipliers, etc.
A generalized block diagram illustrating a typical impulse (comb) generator application is illustrated in FIG. 1 (as will be explained in greater detail below). Note that the circuitry of FIG. 1 (with additional filter coupled to the output of the circuitry) implements a frequency multiplier. Typical yet not an exclusive example of narrow impulses are those that fall in the range of 3-10 GHz. Note also that in many radar and imaging applications the repetition rate of the driving pulses is known to use low. In contrast, applications such as comb generators, multiplier and narrow impulse communication use typically high repetition rate.
It is known in the art to employ a so called Step Recovery Diodes for generating narrow (ultra wideband) impulses. As is generally known per se Step recovery diodes, or SRD's are used as impulse generator (they can be used as high order frequency multipliers and will multiply as high as 20× [when used as a comb generator]). Proper filtering and pulse shaping produces frequency multiplier (the familiar output of sharp, fast rise time pulses—this is generated by the SRD and inductor no need for filter or pulse shaper).
In operation, the SRD can store charge during the positive half of an input sinusoidal signal and then to extract that charge during the negative going half cycle. Consequently, a current pulse with a rise time equivalent to the “snap time” of the diode is generated in the impulse circuit of the pulse generator or comb generator (multiplier). The so generated signal can then be coupled to the desired application.
Bearing this in mind, attention is drawn to FIG. 1, illustrating, schematically, a circuitry for generating a narrow impulse, in accordance with the prior art. Attention is drawn also to FIGS. 2A-C showing simplified waveform signals used associated with the circuitry of FIG. 1.
As shown, the circuitry 11 includes a class A power amplifier 12 amplifying an input sine wave and driving known per se matching circuit 13 which is coupled to SRD 14. The positive half of the input sine wave (21 in FIG. 2A) gives rise to an amplified signal at the amplifier output 15, which, through the matching circuit 13, causes SRD 14 to be charged. When the input sine transients to the negative half (22 in FIG. 2A) the so stored charge is extracted and as a result, current flows through the SRD 14 and the matching circuitry 13 in the direction indicated by arrow 16. The current waveform is depicted schematically as 23 (FIG. 2B). As the current abruptly terminates, a short (ultra wideband) impulse (24, FIG. 2C) is generated over load 17 and fed through output 18 to the desired application such as a comb generator (multiplier).
Note that in order to drive sufficient current into and out of the SRD (e.g. 14 of FIG. 1), the power amplifier(s) has to be high power and requires high current to operate. This would be very inefficient, particularly when the rate of the input is low in the range of 1 MHz to 10 MHz. One of the immediate consequences would be that this high power consumption would adversely affect on the battery life span of any battery operated product accommodating a prior art narrow impulse generating circuitry.
There is thus a need in the art to provide a more efficient circuitry for generating narrow ultra wideband pulses.